I defined BYTE $000A as IFF_HEADS. This value has always been 0 (reserved). The value now represents the heads that are in the image file:

0=both heads1=side 0 (bottom head)2=side 1 (top head)

I did this because there is a big interest right now in Atari 400/800 disks, and it seems silly to image both sides of a single sided disk. I am changing the copier so you can select the heads to be used, and the Atari 400/800, TRS-80, TI-99/4A, and CP/M will default to a single side. You will be able to select 0, 1, or both heads. So, Atari ST disks that are single sided could be imaged that way to save disk space.